Recently, in wireless communication, a retransmission control method that combines propagation path encoding and retransmission composition has called attention as a system implementing high-speed transmission by effectively using the limited frequency band. As a combination of the propagation path encoding and the retransmission composition in a retransmission control method, a combination of a turbo code for which a flexible encoding rate can be set with puncture and an IR (incremental redundancy) method in which a punctured parity bit is slightly added each time when a retransmission occurs is effective. Such a retransmission control method is precisely referred to as Hybrid ARQ (HARQ). However, hereinafter, such a retransmission control method is described simply as “retransmission control”.
In Non Patent Citation 1, as an error correction method using adaptive feedback, technology for improving the error correction capability by using the IR is disclosed. In addition, in 3GPP-LTE (3rd Generation Partnership Project Long Term Evolution) that is a specification of the next cellular system, in order to simplify the definition of retransmission data such as the redundancy version (hereinafter, referred to as RV), CBRM (Circular Buffer based Rate-Matching) is reviewed (see Non Patent Citation 2). The CBRM is a rate matching method in which the RV is defined by sequentially reading out a turbo code accumulated in a circular buffer that is a sequential read-type buffer from any arbitrary start position in order of the buffer address.
An example of the operation of the retransmission control that combines propagation path coding and the retransmission composition will be briefly described with reference to FIG. 15. FIG. 15 is a diagram representing a concrete example of the relationship between transmission data and RV parameter settings in the retransmission control and shows the image of an IR buffer in a case where the encoding rate R=5/6. In the retransmission control using the IR, an RV parameter that represents the start position of the retransmission data for retransmission is set. Thus, on the transmission side, the data from the start position that is designated by the RV parameter is transmitted as the retransmission data, and the receiver side and the reception side is notified of this RV parameter.
When the transmission data is generated on the transmission side, turbo encoding is performed for systematic bits (denoted by S in the figure) in which information to be transmitted is included so as to generate parity bits (in the figure, denoted by P), and the encoded data is stored in the IR buffer. A puncture process is performed for the parity bits of the encoded data inside the IR buffer with a uniform rule, and a part of the encoded data is extracted and transmitted. At the first transmission, the left end in the figure inside the IR buffer is set as the data start position.
FIG. 15 represents a configuration example in which an RV parameter is represented by 2 bits, and a total of four data start positions (in the figure, denoted by white circles) are arranged. In such a case, at the first transmission, RV=0, a part of the systematic bits S and the parity bits P is transmitted from the start position by using all the number of bits that can be transmitted by using predetermined physical resources. Here, the remaining data out of the encoded data inside the IR buffer is handled as untransmitted data. When an Nack signal is fed back from the reception side, and retransmission is to be performed, RV is set as RV=2 as the second transmission data, and data inside the IR buffer is extracted from the third start position from the left side, and a signal is transmitted by using the same number of bits as that of the first transmission. Thereafter, at the third transmission, RV is set as RV=1, at the fourth transmission RV is set as RV=3, and as shown in FIG. 15, data inside the IR buffer is extracted from a respective start position and is transmitted.
In a wireless communication system such as a cellular system, adaptive MCS (Modulation and Coding Scheme) control in which a modulation type and an encoding rate are adaptively changed in accordance with the reception quality is reviewed. In the adaptive MCS control, the encoding rate is changed by puncture or repetition of a bit row after encoding.
[Non Patent Citation 1] David M. Mandelbaun, “An adaptive-feedback coding scheme using incremental redundancy”, Information Theory, IEEE Transactions on, May 1974, P. 388-389
[Non Patent Citation 2] R1-072604, “Way forward on HARQ rate matching for LTE”, Ericsson, et al., 3 GPP TSG-RAN WG1 RAN1#49, 2007/05